Optical storage can be used to achieve high areal density data storage. The areal density of an optical storage device, in principle, may be only limited by the diffraction limit of an illuminating optical beam for reading or writing. Electro-optical data storage systems based on magneto-optical materials can be configured to produce an areal data density of up to or higher than about one gigabit per square inch.
One approach to increase the areal data density in an optical storage system uses a reduced beam size. Due to the diffraction limit, a monochromatic optical beam can be focused to a significantly reduced or minimized beam size on the order of a wavelength. Light sources with short wavelengths, such as those toward the blue end of the optical spectrum, may be used to further decrease the beam size and thereby achieve higher aerial density.
Alternatively, the numerical aperture of the objective lens can be increased to focus a beam of a given wavelength to a smaller spot within the diffraction limit.